Good point. It seems like there is a variation on Poe's Law here, but I can't quite put my finger on it.

It works as a honeypot either way.

On a more practical note, Derek Siver's advice at [1] to ask bidders to post a "magic phrase" of some sort has worked really well for me. I literally just select a couple of random words from /usr/share/dict/words and add something like:

  To prove that you have actually read this listing, please include the words 'FOOLHARDY PARADIGM' somewhere in your response. Any bid that does not include these words will be ignored.

prominently in the listing. You might be surprised how many responses that filters out. I was a little surprised at how legitimate some of the automated (or at least, thoughtless) responses seemed to be. I almost certainly would have wasted time on some of those without this little test. (I probably rejected some responses from real people too, but evidently people with insufficient attention to detail.)

[1] http://sivers.org/how2hire